Absorption	A mode of entry of a toxic substance into the body in which the substance enters through the unbroken skin.
ACGIH	American Conference of Governmental Industrial Hygienists
Acute	A health effect that is the result of a short time exposure to a very high concentration of a toxic material. The effect is usually immediately seen, not more than several hours after the exposure.
Adequate Ventilation	Ventilation that will keep the exposures to a material below the Threshold Limit Value.
Administrative Control	A method of reducing the total exposure or dose to a worker by lowering the amount of time the worker is exposed.
Anesthetic	A material that causes unconsciousness after excessive exposure. The effect is the same as that of drugs used for surgery.
Asphyxiation	Smothering. A toxic material may cause asphyxiation by diluting the amount of oxygen in the air, paralyzing the lungs, or interfering with the body's ability to transport oxygen to the cells.
Boiling Point	The temperature at which the vapor pressure of a liquid equals atmospheric pressure or at which the liquid changes to a vapor. The boiling point is usually expressed in degrees Fahrenheit. If a flammable materials has a low boiling point, it indicates a special fire hazard.
Carcinogen	A material that can cause cancer.
C.A.S. Number	Identifies a particular chemical by the Chemical Abstracts Service, a service of the American Chemical Society that indexes and compiles abstracts of worldwide chemical literature called "Chemical Abstracts."
Chronic	A toxic effect that occurs only after exposure to a material for a long time, usually months or years. The amount of exposure is usually very low, and often symptoms are not immediately noticeable.
Combustible	According to the DOT and NFPA, combustible liquids are those having a flash point at or above 100 degrees Fahrenheit (38 degrees Celcius), or liquids that will burn. They do not ignite as easily as flammable liquids. However, combustible liquids can be ignited under certain circumstances, and must be handled with caution. Substances, such as wood, paper, etc., are termed "Ordinary Combustibles."
Concentration	The amount of material in the air, eg., 50 parts per million. May also refer too the amount of a substance in a mixture, eg., 10% ammonia in water.
Control	A method of limiting or eliminating exposure of workers to a hazardous substance.
Cumulative Effect	An effect of a toxic material that takes place only after a quantity of the material is taken into the body, or when damage is caused by the substance over a period of time at a rate faster than the body can repair the damage.
Decompose	Breaking down of a chemical under heat, shock, or mixing with other chemicals. The resulting products of decomposition may be more toxic or hazardous than the original substance.
Dose	The amount of a substance that enters the body. The amount depends on the rate at which the substance enters the body and the length of time the substance continues to enter the body, eg., a worker may inhale 10 milligrams of dust per day for 10 days. The total dose is 100 milligrams. Not all of the substance may remain in the body; some is eliminated, possibly as fast as it enters.
DOT	Department of Transportation. A Federal Agency which specifies a labeling system for the interstate transport of hazardous materials, among other duties.
Dust	Relatively large particles of solid material in the air, generated by grinding or crushing.
Engineering Control	A change in equipment, materials or process, eg., ventilation, that reduces the hazard from the substance.
EPA	The Environmental Protection Agency is the governmental agency responsible for administration of laws to control and/or reduce pollution of air, water, and land systems.
EPA Number	The number assigned to chemicals regulated by the EPA.
Epidemiology	The study of disease in human populations.
Evaluation	The process used by a Safety or Health Professional to determine the extent of hazard presented by the use of a toxic material. It often involves taking air samples to determine total dose.
Exposure	Similar to dose. The combination of concentration of a substance in air and the amount of time a worker is exposed to that concentration gives the total exposure or dose.
Flammable Limits	The range of concentrations in air of flammable vapors of a substance between which the vapors will ignite and continue to burn; possibly resulting in an explosion. The lower limit is the Lower Flammable (or explosive) Limit, LFL, and the upper limit is the Upper Flammable (or explosive) Limit, UFL. Below the LFL, there is not enough vapor to support combustion. Above the UFL there is too much vapor. The mixture is too much to burn. NOTE: The MSDS uses Explosive Limit, but the preferred term is Flammable Limit. The terms are synonymous.
Flammable Liquid	According to the DOT and NFPA a flammable liquid is one that has a flash point below 100 Fahrenheit. (See FLASH POINT.)
Flash Point	The temperature at which enough vapor is produced from a flammable liquid to reach a concentration equal to the LFL, (See FLAMMABLE LIMITS). A substance with a high flash point is less hazardous than one with a low flash point.
Fume	A term used by health professionals to mean solid particles in air, usually much smaller than dust, and generaed by heating a solid material, eg., a welding rod.
Gas	A substance like air. Nitrogen, oxygen and carbon dioxide are gases.
Hazard	A term that combines the ability or potential of a substance or process to cause a problem with the probability that the substance actually will cause a problem, eg., gasoline is a flammable substance. If small amounts are kept in sturdy, sealed containers with no ignition sources nearby, the hazard is small. If gasoline is kept in large, open buckets and smoking and welding are done nearby, the hazard is great.
Individual Susceptibility	The difference in reaction to a give dose of a toxic material by different individuals. Some persons may show a stronger or more noticeable effect from the same dose than others. Such individuals may be allergic or hypersensitive to the material.
Incompatible	Two or more chemicals that will produce an undesirable reaction when mixed, eg., mixing any acid with sodium cyanide will produce highly toxic hydrogen cyanide gas.
Infrared	A type of radiation give off by a hot stove or the sun, sensed as heat.
Ingestion	Swallowing. One of the ways a toxic substance can enter the body.
Inhalation	Breathing in. The most common way for a toxic substance to enter the body.
Irritant	A substance that produces an irritating effect when it contacts skin, eyes, nose, or respiratory system.
Isolation	A method of control for hazardous materials in which the material is kept completely away from workers by enclosing it in tanks, pipes, or reaction vessels.
Lethal Concentration 50 (LC50)	The concentration of an air contaminant that will kill 50% of the test animals in a group within the first 30 days following exposure.
Lethal Dose 50 (LD50)	The dose of a substance or chemical that will kill 50% of the test animals in a group within the first 30 days follwoing exposure.
LFL or LEL	Lower Flammable Limit or Lower Explosive Limit.
Local Exhaust Ventilation	(Also known as exhaust ventilation.) A ventilation system that captures and removes the contaminants at the point they are being produced before they escape into the workroom air. The system consists of hoods, duckwork, a fan and possibly an air cleaning device. Advantages of local exhaust ventilation over general ventilation include: It removes the contaminant rather than dilutes it; it requires less airflow and thus is more economical over the long term; and the system can be used to conserve or reclaim valuable materials. However, the system must be properly designed with the correctly shaped and placed hoods; and correctly sized fans and duckwork.
MCA	Manufacturing Chemists Association
Microorganism	Germs, bacteria, viruses, yeasts, molds, and fungi are capable of causing disease. These are biological hazards.
Microwaves	A type of radiation used for heat sealers, ovens, radar, and communications. A physical hazard.
Mist	Liquid droplets in air.
MSDS	Material Safety Data Sheet.
Mutagen	Anything that can cause a change (or mutation) in the genetic material of a living cell.
Narcosis	Stupor or unconsciousness caused by exposure to a chemical.
NFPA	The National Fire Prevention Association is a voluntary membership organization whose aims are to promote and improve fire protection and prevention. NFPA has published 16 volumes of codes known as the National Fire Codes. Within these codes is a Standard No. 704, "Identification of the Fire Hazards of Materials." This is a system that rates the hazard of a material during a fire. These hazards are divided into health, flammability, and reactivity hazards and appear in a well-known diamond system using numbers from 0 to 4 to indicate the severity of the hazard. Zero indicates no special hazard and four indicates severe hazard.
NIOSH	The National Institute for Occupational Safety and Health is a federal agency that among its various responsibilites, trains occupational health and safety professionals; condcuts research on health and safety concerns; and tests and certifies respirators for workplace use.
Nonionizing Radiation	Forms of radiation, eg., infrared, radio and microwaves.
NPCA	National Paint Coatings Association
Odor Threshold	The minimum concentration of a substance at which a majority of test subjects can detect and identify the substance's characteristic odor.
OSHA	Occupational Safety and Health Administration. This Federal agency is responsible for promulgating standards to provide a safe and healthy work environment.
Oxidizer	Is a substance that gives up oxygen easily to stimulate combustion of organic material.
Oxygen Deficiency	An atmosphere having less than the normal percentage of oxygen found in normal air. Normal air contains 21% oxygen at sea level.
Permissilbe Limit Exposure, PEL	OSHA's number that tells the concentration of a chemical in air that a worker may breathe for a given period of time, without experiencing adverse effects, (see TLV).
ppm	Parts (of vapor or gas) per million (parts of air) by volume.
Personal Protective Equipment	Any device or clothing worn by the worker to protect against hazards in the environment. Examples are respirators, gloves, and chemical splash goggles.
Polymerization	A chemical reaction in which two or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules. A hazardous polymerization is the above reaction, with an uncontrolled release of energy.
Reactive	A chemical that will undergo undesirable changes or reactions when heated, shocked, exposed to air, or mixed with other substances, (see INCOMPATIBLE).
Recognition	The process of identifying potential hazards. The process of evaluation then assesses the degree of actual hazard.
Respirator	A device worn over the face and used to either mechanically filter dirty air or supply fresh air to the wearer.
Respiratory Hazard	A particular concentration of an airborne contaminant that, when it enters the body by way of the respiratory system or by being breathed into the lungs, results in some bodily function impairment.
Sensitizer	A substance that may cause no reaction in a person during initial exposures, but afterwards, further exposures will cause an allergic response to the substance.
Short Term Exposure Limit	Represented as STEL or TLVSTEL, this is the maximum concentration to which workers can be exposed for a short period of time (15 minutes) for only four times throughout the day with at least one hour between exposures. Also the daily TLVTWA must not be exceeded.
Solvent	A liquid used to dissolve or clean materials. Water is a solvent; but materials like alcohol, trichloroethylene, or methyl ethyl ketone are usually referred to as solvents or organic solvents. These materials usually evaporate into the air and can be inhaled into the body.
Specific Gravity	The density of a liquid when compared to water which has a specific gravity of 1.0. A liquid with a specific gravity of less than 1 will float on water; while one with a specific gravity of more than 1 will sink in water.
Static Grounding	A means of grounding a flammable liquid storage container to prevent the accumulation of a static electrical charge.
Substitution	A control of grounding a flammable liquid storage container to prevent the accumulation of a static electrical charge.
Systemic Poisoning	A toxic effect on the body in which one or more organs are damaged by a substance, e.g., lead entering the body by inhalation can damage the nervous system, the kidneys, the bone marrow or the intestines.
Teratogen	An agent or substance that may cause physical defects in the developing embryo or fetus when a pregnant female is exposed to that substance.
Threshold Limit Value (TLV)	A number that tells the concentration of a chemical in air that a worker may breathe for a given period of time (a dose) without experiencing adverse effects. The American Conference of Governmental Industrial Hygienists, ACGIH, publishes TLVs for about 500 substances. OSHA uses similar limits called Permissible Exposure Limits, PEL.
Time Weighted Average	The average time, over a given work period (e.g., 8 hour work day), of a person's exposure to a chemical or an agent. The average is determined by sampling for the contaminant throughout the time period. Represented as TLV-TWA.
Toxic	Capable of causing damage to the body. A substance is more toxic if a small amount can cause the damage. The degree of hazard of a substance depends partly on how toxic it is.
Trade Secret	An ingredient of a chemical that gives the producer or manufacturer a business advantage over competitors. According to the OSHA Hazards Communication Standard, a manufacturer does not have to disclose the chemical name of a substance in the product if it is a trade secret. Sufficient information must still be provided to ensure safe use of the product.
UFL or UEL	Upper Flammable Limit or Upper Explosive Limit.
Unstable	A chemical that will decompose or react very easily. Nitroglycerine is unstable because it will explode when shocked by dropping a container.
Vapor	A substance in air similar to a gas, but produced by the evaporation of a liquid into the air. Solvents usually enter the body in the form of a liquid.
Vapor Density	A measure of how heavy the vapor of a liquid is, compared to air which has a vapor density of 1.0. When the vapor density is high, the vapors will tend to collect in low spots.
Vapor Pressure	A measure of the volatility of ease with which a liquid will evaporate to become a vapor. A high vapor pressure means the liquid evaporates quickly.